Photo-patterned silicone bump bonds for sensor interconnects

Bump bonding is the standard approach for connecting pixel sensors with read-out ASICs. Current fine-pitch bump bonds lead to permanent bonds. We use photo-patternable silicone (polydimethylsiloxane, or PDMS) in combination with a metal coating to generate flexible and reversible bump bonds. This process requires only a relatively low temperature, <150°C, and leads to very homogeneous bump height, because the PDMS is applied by spin-coating. The technique is also applicable to brittle materials, where wire-bonding is problematic, such as gamma-ray detectors based on CdZnTe and CdTe. This paper describes the general concept and presents first results.